Amorphous polypropylene stabilized hot melt adhesive

ABSTRACT

Hot melt adhesive compositions with resistance to crusting and stable viscosity characteristics are prepared from a mixture of ethylene-vinyl acetate copolymer, glycerol ester of hydrogenated rosin, wax, and amorphous polypropylene. The improved hot melt adhesive formulation can contain from about 30 to about 50 percent by weight ethylene-vinyl acetate copolymer, from about 20 to about 40 percent by weight of glycerol ester of hydrogenated rosin, from about 20 to about 40 percent by weight of a wax, and from about 10 to about 30 percent by weight amorphous polypropylene.

United States Patent [191 Jurrens [54] AMORPHOUS POLYPROPYLENESTABILIZED HOT MELT ADHESIVE [75] Inventor: LawrenceD. Jurrens,Bartlesville,

Okla.

[73] Assignee: Phillips Petroleum Co. 22 Filed: Ma '2'8,i9'71 21 Appl.No.: 148,115

[52] US. Cl ..260/27 EV, 260/28.5 A, 260/897 A 3,360,488 12/1967 Hall.;....260/23 Feb. 20, 1973 3,539,481 11/1970 Parker ..260/27 PrimaryExaminer-Donald E. Czaja Assistant Examiner-William E. ParkerAtt0rneyYoung and Quigg [5 7 ABSTRACT Hot melt adhesive compositionswith resistance to crusting and stable viscosity characteristics areprepared from a mixture of ethylene-vinyl acetate copolymer, glycerolester of hydrogenated rosin, wax, and amorphous polypropylene. Theimproved hot melt adhesive formulation can contain from about 30 toabout 50 percent by weight ethylene-vinyl acetate copolymer, from about20 to about 40 percent by weight of glycerol ester of hydrogenatedrosin, from about 20 to about 40 percent by weight of a wax, and

from about 10 to about 30 percent by weight- AMORPHOUS POLYPROPYLENESTABILIZED HOT MELT ADHESIVE BACKGROUND OF DISCLOSURE This invention isrelated to hot melt adhesive compositions. In another aspect, thisinvention is related to hot melt adhesives having resistance to crustformation. In another aspect, this invention is related to hot meltadhesives having improved resistance to viscosity increase caused byheat aging. In still another aspect, it is related to hot melt adhesiveformulations based on amorphous polypropylene.

A hot melt adhesive melts sharply upon heating and flows freely for easyapplication to the substrate which is to be bonded. Hot melt adhesivesare not dependent on cross-linking or other chemical reactions toproduce a bond between the substrate materials. The bond is producedupon cooling and is dependent upon the penetration of the surface of thesubstrate. These adhesives are particularly useful in bonding paper,plastics, textiles, wood and other porous materials. I-lot meltadhesives are particularly useful for sealing folding cartons and in theproduction of corrugated paperboard cartons.

One of the problems frequently associated with hot melt adhesives,particularly those formulations containing ethylene-vinyl acetatecopolymers, is a tendency toward increased viscosity on being held at anelevated temperature, as in a hot melt applicator, for an extendedlength of time. These hot melt adhesives also tend to form a crust onthe surface of the hot melt adhesive upon heat aging in the hot meltapplicator. This crust is particularly bothersome in breaking andplugging the applicator during the operation of applying the hot meltadhesive to a surface. Accordingly, I have now discovered useful hotmelt adhesive formulations based on the combination of a low molecularweight amorphous polypropylene and an ethylene-vinyl acetate copolymerwhich have increased resistance to viscosity increase on heat aging andto the formation of a crust.

An object of this invention is to provide hot melt adhesive compositionswhich do not form a crust when subjected to heat aging.

Other aspects, objects as well as the several advantages of thisinvention will be apparent to those skilled in the art upon reading thespecification and the appended claims.

SUMMARY OF THE INVENTION In accordance with this invention, hot meltadhesive compositions with superior resistance to heat aging areprepared by combining amorphous polypropylene having a molecular weightof less than 10,000, an ethylenevinyl acetate copolymer, a wax and aglycerol ester of a hydrogenated rosin. l have found that compositionsof my invention can be held at elevated temperatures in a hot meltapplicator without materially changing the viscosity and withoutformation of a crust. Thus, these compositions have the distinctadvantage of added ease of application over ethylene-vinyl acetatecopolymer based hot melt adhesives currently in use.

The ethylene-vinyl acetate copolymers suitable for this invention can beany copolymer having in the range from about to about 35 percent vinylacetate in the copolymer. A presently preferred copolymer contains about17 to about 19 percent vinyl acetate in the copolymer. Theethylene-vinyl acetate copolymer can comprise from about 30 to about 50weight percent of the total composition. It is presently preferred thatabout 35 to about 45 percent by weight of the total composition becomprised of ethylene-vinyl acetate copolymer.

Suitable rosin tackifiers can be employed in the hot melt adhesivecompositions of this invention including 1 natural rosins, such as gumrosin, wood rosin, and tall oil rosin; hydrogenated rosins, such ashydrogenated wood, gum, and tall oil rosins; esters of rosins, such asmethyl and glycerol esters of wood rosin, gum rosin and hydrogenatedrosin. A glycerol ester of hydrogenated rosin is the preferred rosintackifier for use in this invention. Rosin tackifier can advantageouslybe added in amounts ranging from 20 to about 40 percent by weight of thetotal composition, preferably in the range of about 25 to about 35percent by weight.

Waxes and wax-like materials including, for example, petroleum waxes,such as paraffin and microcrystalline wax, or synthetic waxes such asFischer-Tropsch wax are advantageously added to compositions of thisinvention in amounts ranging from about 20 to about 40 percent by weightof the total composition. A preferred range for these additives is fromabout 25 to about 35 percent by weight of the total composition.

The noncrystalline polypropylene suitable for this invention has amolecular weight, calculated from intrinsic viscosity, of less than10,000 preferably in the range of 7,000 to 8,000 and is soluble inhydrocarbon solvent such as pentene at the boiling point. This materialhas a crystallinity of less than about 5 percent. The amorphouspolypropylene makes up from about 10 to about 30 percent by weight ofthe total formulation. Preferably from about 15 to about 25 percent byweight of the formulation is amorphous polypropylene.

An antioxidant or antioxidant formulation can be added to the hot meltadhesive composition if desired. A finite amount of antioxidant up toabout 0.5 weight percent of the total hot melt adhesive composition hasbeen found to be effective. A butylated hydroxytoluene producedcommercially has been found to be a particularly effective antioxidant(available from I-Iercules Inc. under the designation Dalpac R).

Mixing the components can be carried out in any suitable manner whichcontinues the mixing at a temperature elevated sufficiently to maintainthe components in a molten state until the adhesive composition ishomogeneous. Satisfactory mixing can be accomplished with a heated blademixer or in a container maintained in an oil bath at a temperaturebetween 390 and 455F.

The following examples of the formulation of the adhesive of thisinvention, the description of the test procedures and the data derivedtherefrom are meant to be exemplary and are not exclusive.

EXAMPLE I Adhesive formulations were prepared by melting the componentin a stainless steel beaker heated in an oil bath maintained at atemperature of 400F. Elvax 410, a polyethylene-vinyl acetate copolymercontaining 17 to 19 percent by weight vinyl acetate made by DuPont,

Staybelite Ester 10, a glycerol ester of hydrogenated rosin made byHercules, and a paraffin wax melting at 150F were combined withagitation until a homogeneous blend was attained. Where applicable,additional paraffin wax or amorphous polypropylene having an EXAMPLE llSamples of the material prepared as in Example 1 were placed in 400milliliter stainless steel beakers and aged in an air-draft oven for 100hours at 350F. The tables below show the results of these tests.

TABLE I lnit. Visc. At Adhesive Formulation Vise. 350F after CrustPercent by Weight at 350'} 100 Hrs. Format 350F. ation A B C D 40 30 305 I2 524 Hard Crust 35 40 25 280 280 Hard Crust 35 25 25 15 400 368 NoCrust A ethylene-vinyl acetate copolymer B paraffin wax C glycerol esterof hydrogenated rosin D amorphous polypropylene The table aboveillustrates that a hard crust forms on a melt adhesive sample after heataging using a melt adhesive sample composed of the standard formulationof ethylene-vinyl acetate copolymer, paraffin and a glycerol ester ofhydrogenated rosin. Increasing the relative amount of paraffin waximproves the viscosity on heat aging but does not stop the formation ofa crust. The addition of amorphous polypropylene to the formulationprevents the formation of a crust after heat aging without increasingthe viscosity.

TABLE II Visc. adhesive formulation after crust Percent by Weight init.)0 hrs. formvisc. at 350F ation A B C D 4030 30 67203 20F 6800320? hard6000330F 5840330F crust 5200340F 5360340F 3727 27 9 5920320? 5360320Fhard 5120330F 4800330F crust 44003401 4480340F 3224 24 20 4800320F4640320F No 4240330"! 4000330? crust 3600340F 3280340F A ethylene-vinylacetate copolymer B paraffin wax C glycerol ester of hydrogenated rosinD amorphous polypropylene This table illustrates the prevention of crustformation by increased addition of amorphous polypropylene withoutmaterially altering the viscosity of the melt even after prolongedaging.

4 TABLE III adhesive formulation visc. after crust percent by weightinit. vise. hrs. formation A B C D 37 27 27 9 4400340F 4480340F hardcrust 35 25 25 15 4000350F 3680350F no crust 32 24 24 20 3600340F3280340F no crust A ethylene-vinyl acetate copolymer 8 parafiin wax Cglycerol ester of hydrogenated rosin D amorphous polypropylene The tableabove illustrates the prevention of formation of crust after heat agingby including amorphous polypropylene in a hot melt adhesive formulationusing the ranges prescribed in this invention, without effecting anymaterial change in viscosity.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure, and the appended claims to the invention theessence of which is that there has been provided a hot melt adhesivecomposition with improved heat aging characteristics and prevention ofcrust formation based on a mixture of amorphous polypropylene,ethylene-vinyl acetate copolymer, wax, and glycerol ester ofhydrogenated rosin.

I claim:

1. A hot melt adhesive composition comprising (1) about 10 to about 30percent by weight amorphous polypropylene having a molecular weight ofless than 10,000; (2) about 20 to about 40 percent by weight of a wax;(3) about 20 to about 40 percent by weight of a rosin tackifier and (4)about 30 to about 50 percent by weight of an ethylene-vinyl acetatecopolymer.

2. The hot melt adhesive composition of claim 1 wherein an antioxidantformulation in the range of up to 0.5 percent by weight of the totalweight of the formulation is present in the composition.

3. A hot melt adhesive composition of claim 1 wherein the amorphouspolypropylene has a molecular weight in the range of 7,000 to 8,000 andhas a crystallinity of less than 5 percent.

4. A hot melt adhesive composition of claim -1 wherein theethylene-vinyl acetate copolymer contains about 17 to about 19 percentvinyl acetate.

5. A hot melt adhesive composition of claim 1 comprising about 30 toabout 40 percent by weight ethylene-vinyl acetate copolymer, about 20 toabout 30 percent by weight paraffin wax, about 20 to about 30 percent byweight rosin tackifier and about 15 to about 25 percent by weightamorphous polypropylene.

6. A hot melt adhesive composition of claim 1 comprising 32 percent byweight ethylene-vinyl acetate copolymer, 24 percent. by weight paraffinwax, 24 percent by weight glycerol ester of hydrogenated rosin, and 20percent by weight amorphous polypropylene.

7. A hot melt adhesive composition of claim 1 comprising 35 percent byweight ethylene-vinyl acetate copolymer, 25 percent by weight paraffinwax, 25 percent by weight glycerol ester of hydrogenated rosin, and 15percent by weight amorphous polypropylene.

1. A hot melt adhesive composition comprising (1) about 10 to about 30percent by weight amorphous polypropylene having a molecular weight ofless than 10,000; (2) about 20 to about 40 percent by weight of a wax;(3) about 20 to about 40 percent by weight of a rosin tackifier and (4)about 30 to about 50 percent by weight of an ethylene-vinyl acetatecopolymer.
 2. The hot melt adhesive composition of claim 1 wherein anantioxidant formulation in the range of up to 0.5 percent by weight ofthe total weight of the formulation is present in the composition.
 3. Ahot melt adhesive composition of claim 1 wherein the amorphouspolypropylene has a molecular weight in the range of 7, 000 to 8,000 andhas a crystallinity of less than 5 percent.
 4. A hot melt adhesivecomposition of claim 1 wherein the ethylene-vinyl acetate copolymercontains about 17 to about 19 percent vinyl acetate.
 5. A hot meltadhesive composition of claim 1 comprising about 30 to about 40 percentby weight ethylene-vinyl acetate copolymer, about 20 to about 30 percentby weight paraffin wax, about 20 to about 30 percent by weight rosintackifier and about 15 to about 25 percent by weight amorphouspolypropylene.
 6. A hot melt adhesive composition of claim 1 comprising32 percent by weight ethylene-vinyl acetate copolymer, 24 percent byweight paraffin wax, 24 percent by weight glycerol ester of hydrogenatedrosin, and 20 percent by weight amorphous polypropylene.